* Fix boot warnings and firewall cellular IPv6
- rules.v6: drop incoming cellular traffic over IPv6 too, rules.v4 only covered IPv4
- sshd: drop the DSA host key, OpenSSH no longer generates or loads them
- sysctl: don't set fs.protected_fifos, fs.protected_regular or kernel.yama.ptrace_scope, the kernel doesn't have them
- udev: only set max_brightness_percent permissions where the attribute exists
- udev: don't ask systemd to start the masked systemd-backlight
* Drop sysctl changes